Obama campaign manager Jim Messina is confident the president has the upper edge in early voting in Ohio, but there are signs of weakness. Photograph: Jason Reed/Reuters

Barack Obama returned to the crucial battleground state of Ohio on Friday following his storm-induced break from campaigning, with a sharpened rhetoric as he scrambles for the finishing line now just four days away.

In the first of three stops in Ohio on Friday, Obama poured scorn on Mitt Romney in front of a barn full of about 5,000 supporters in Hilliard outside the state capital Columbus.

"Governor Romney is a very talented salesman," he said. "He has tried as hard as he can to repackage his old policies and offer them as change."

Obama ridiculed Romney's recent attempt to cast himself as the candidate who would bring change to Washington, accusing him of misleading the American people. "Trying to massage the facts, that ain't change, that's …"

"Lying!" chanted the crowd obligingly.

Obama made a particular bid to woo employees of the car industry who represent one in eight of the Ohio workforce. "The American auto industry is back on top," he said, an allusion to the federal bailout that he authorised.

He also referred to Friday's US employment figures that showed 171,000 new jobs in October – an increase, Obama pointed out, greater "than at any time in the last eight months".

Both presidential candidates are now going hell to leather for the Ohio vote. The reason is simple: taking the White House will be difficult without this state's 18 electoral votes out of the 270 needed to win. In Romney's case it is particularly urgent – no Republican president has attained the highest office without first winning this state.

All recent polls, with the exception of Rasmussen, put Obama in the lead in Ohio, but the advantage is in most cases within the margin of error which is why both presidential candidates will be running around the state in the sort of frenzy normally only seen in children's animations.

Obama will be in Ohio on each of the final days of campaigning, in addition to dashes to Colorado, Florida, Iowa, New Hampshire, Virginia and Wisconsin. To add stardust to proceedings, he is dragging Stevie Wonder on stage with him on Sunday in Cincinnati, and Jay-Z and Bruce Springsteen in Columbus on Monday evening.

Romney too is going for star power, in bucket loads. On Friday night he is staging a mega-rally in West Chester in west Ohio that will pack in almost 100 senior Republican politicians including former secretary of state Condoleezza Rice, former New York mayor Rudy Giuliani, governors Rick Perry and Bobby Jindal, and for good measure the golfer Jack Nicklaus.

The purpose of all this frenetic activity is not to persuade any undecided voters still standing. "I don't know that there are any truly undecided voters right now – this race has been very polarising," said Joe McNamara, president of the city council of Toledo, a Democratic stronghold in north-west Ohio.

The intention, rather, is to energise the Democratic and Republican base so that supporters get out and volunteer in the final three days. Obama made his bid to fire up the base at the Hilliard rally by painting his rival as a bastion of the greedy rich.

"The folks at the top in this country don't need another champion in Washington. They already have a seat at the table," he said.

He warned the crowd that the Republicans were trying to wear the American electorate down so that they didn't bother to vote. "In other words, Ohio, their bet is on cynicism. My bet is on you."

As the presidential race turns to its ultimate stage – the all-important drive to get out the vote – Obama has an inbuilt head start. He has been campaigning in Ohio for 18 months, far longer than Romney who was distracted for months by the primary race, and on the ground has 130 offices spread throughout the state to his rival's 40.

But doubts still remain that Obama will be able to enthuse his followers to the giddy heights that he achieved in 2008. Jim Messina, the Obama campaign manager, insists enthusiasm levels are equivalent to four years ago, and he has also claimed that the president has the upper edge in early voting in Ohio.

But there are signs of weakness in some parts of the state. A politician in a key urban area where Democratic candidates traditionally do well told the Guardian that the Obama campaign was struggling to fill volunteer rotas. Phone banking was being switched to supporters in other states to free up bodies on the ground in Ohio, and volunteer canvassers are being bussed in this weekend from as far away as Brooklyn.

"We have been genuinely surprised by the lack of enthusiasm we've found. The Obama ground game is going to be better than the Republicans', no doubt about that, but not by the degree it was four years ago," said the politician, who asked not to be named.

The Romney campaign also claims to have its base fired up following the televised presidential debates last month. But on the Republican side it is unclear whether they have managed to build on that momentum and it remains to be seen whether they can convert it into extra votes.

The truth is that as they hurtle up the home stretch, both campaigns are depending on the exceptional fortitude of their most loyal followers. Individuals such as Sheila Oxsher, who has turned up at her local campaign office in Columbus every day since mid-August to volunteer for Romney.

She works up to 12 hours a day, seven days a week, and has so far logged 14,707 phone calls to potential Republican voters. "This is my patriotic commitment – it's my equivalent of George Washington crossing the Delaware in 1776," she says.

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